Clinical Experimental Oncology Laboratory, National Cancer Centre Giovanni Paolo II, Bari, Italy.
J Cell Physiol. 2011 Jul;226(7):1934-9. doi: 10.1002/jcp.22524.
K-RAS and BRAF gene mutations are mandatory to set anti-EGFR therapy in metastatic colorectal cancer (mCRC) patients. Due to the relationship of these mutations with tumor epigenotype, we hypothesized the potential role of oncosuppressor methylation of genes involved in K-RAS/BRAF pathway (CDKN2A, RASSF1A, and RARbeta suppressor genes) in inhibiting EGFR signaling cascade. Primary tumor and synchronous liver metastatic tissues of 75 mCRC patients were characterized for promoter methylation by QMSP and for K-RAS and BRAF mutations. RARbeta, RASSF1A, and CDKN2A genes were methylated in 82%, 35%, and 26% of primary tumors, respectively. RASSF1A resulted significantly more frequently methylated in liver metastasis than in primary site (P=0.015), while RARbeta was significantly lower methylated in distant metastasis (P=1.2 × 10(-6)). As regards methylation content, RASSF1A methylation status was significantly higher in liver metastasis with respect to primary tumor (P=0.000) underlying the role of this gene in liver metastatic progression. In our series K-RAS and BRAF were mutated in 39% and 4% of cases, respectively. Methylation frequencies seemed to be unrelated to gene mutations; on the other hand, RASSF1A mean content methylation resulted significantly higher in liver than in primary tumor (288.78 vs. 56.23, respectively, P=0.05) only in K-RAS wild-type cases sustaining a specific role of this gene in metastatic site thus supporting its function in strengthening the apoptotic role of K-RAS. These evidences held the role of oncosuppressor methylation in both colon tumorigenesis and progression and suggested that epigenetic events should be taken into account when biological therapies in mCRC patients have to be set.
K-RAS 和 BRAF 基因突变是为转移性结直肠癌 (mCRC) 患者设定抗 EGFR 治疗的必要条件。由于这些突变与肿瘤表型有关，我们假设 K-RAS/BRAF 通路中参与基因的肿瘤抑制因子甲基化（CDKN2A、RASSF1A 和 RARβ 抑制剂基因）在抑制 EGFR 信号级联反应中可能发挥作用。通过 QMSP 对 75 名 mCRC 患者的原发肿瘤和同步肝转移组织进行了启动子甲基化特征分析，并对 K-RAS 和 BRAF 突变进行了分析。RARβ、RASSF1A 和 CDKN2A 基因在原发性肿瘤中的甲基化率分别为 82%、35%和 26%。RASSF1A 在肝转移中比在原发性肿瘤中更频繁地发生甲基化（P=0.015），而 RARβ 在远处转移中明显低甲基化（P=1.2×10(-6)）。就甲基化含量而言，RASSF1A 在肝转移中的甲基化状态明显高于原发性肿瘤（P=0.000），这表明该基因在肝转移进展中起作用。在我们的研究中，K-RAS 和 BRAF 分别在 39%和 4%的病例中发生突变。甲基化频率似乎与基因突变无关；另一方面，RASSF1A 的平均含量甲基化在肝转移中明显高于原发性肿瘤（分别为 288.78 与 56.23，P=0.05），仅在 K-RAS 野生型病例中，这支持了该基因在转移部位的特定作用，从而支持其在增强 K-RAS 凋亡作用方面的功能。这些证据支持了肿瘤抑制因子甲基化在结肠癌发生和进展中的作用，并表明在为 mCRC 患者制定生物治疗时应考虑表观遗传事件。
